!     
!     CalculiX - A 3-dimensional finite element program
!     Copyright (C) 1998-2018 Guido Dhondt
!     
!     This program is free software; you can redistribute it and/or
!     modify it under the terms of the GNU General Public License as
!     published by the Free Software Foundation(version 2);
!     
!     This program is distributed in the hope that it will be useful,
!     but WITHOUT ANY WARRANTY; without even the implied warranty of 
!     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 
!     GNU General Public License for more details.
!     
!     You should have received a copy of the GNU General Public License
!     along with this program; if not, write to the Free Software
!     Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
!
!     author: Yannick Muller
!
      real*8 function calc_residual_wye(pt1,Tt1,xflow1,xflow2,
     &pt2,Tt2,ichan_num,A1,A2,A_s,dh1,dh2,alpha,zeta_fac,kappa,
     &R,ider,iflag,zeta)
!
      implicit none
!
      integer icase,ichan_num,icrit1,icrit2,ider,iflag
!
      real*8 
!     In- and Output
     &f,
     &R,
!
!     Kappa stuff
     &kappa,
!
     &pt1,
     &pt2,
     &Tt1,
     &Tt2,
     &xflow1,
     &xflow2,
!
     &zeta,
!
     &A1,
     &A2,
     &A_s,
!
     &Ts1,
     &Ts2,
     &Ts_s,
     &dh1,
     &dh2,
     &alpha,
     &Q_crit,
     &pspt_crit,
     &Q0,
     &Q1,
     &Q2,
     &pspt0,
     &pspt1,
     &w1,
     &w2,
     &w1w2,
     &w2w1,
     &VsV1,
     &pi,
     &z2d390,
     &z1p090,
     &z60,
     &z90,
     &hq,
     &Ts0,
     &zeta_fac,
     &M1,
     &M2,
     &pspt2
!
      real*8 Table_A(2,11)
!
      icrit1 = 0
      icrit2 = 0
!
!     setting icase (always adiabatic)
      icase=0;
!
      pi=4.d0*datan(1.d0)
      Q_crit = dsqrt(kappa/R)*
     &   (1+0.5d0*(kappa-1))**(-0.5d0*(kappa+1)/(kappa-1))
      pspt_crit = (2/(kappa+1)) ** (kappa/(kappa-1))
!
      Q0 = xflow1*dsqrt(Tt1)/pt1/A1
      Q1 = xflow2*dsqrt(Tt1)/pt1/A2
      if(Q1.ge.Q_crit) then
         Q1 = Q_crit
         icrit1 = 1
         write(*,*)'*WARNING in Wye:'
         write(*,*)'Critical conditions at 1'
      endif
      Q2 = xflow2*dsqrt(Tt1)/pt2/A2
      if(Q2.ge.Q_crit) then
         Q2 = Q_crit
         icrit2 = 1
         write(*,*)'*WARNING in Wye:'
         write(*,*)'Critical conditions at 2'
      endif
!
!     Flow velocity at inlet
      Ts0=Tt1
     
      call ts_calc(xflow1,Tt1,pt1,kappa,r,A1,Ts0,icase)
      pspt0 = (Ts0/Tt1)**(kappa/(kappa-1))
      call wpi(w1, pspt0, Q0, 
     &      dsqrt(Tt1),kappa,R) 
!
!     Flow velocity at outlet
      call ts_calc(xflow2,Tt1,pt1,kappa,r,A2,Ts1,icase)
      pspt1 = (Ts1/Tt1)**(kappa/(kappa-1))
      call wpi(w2, pspt1, Q1, 
     &      dsqrt(Tt1),kappa,R) 
!
c      w2w1=w2/w1
c      w1w2=w1/w2
      if(w2.eq.0.d0)then
         w1w2=1d30
      else
         w1w2=w1/w2
      endif
      if(w1.eq.0.d0)then
         w2w1=1d30
      else
         w2w1=w2/w1
      endif
!
!     Zeta calculation
!     Main branch
      if(ichan_num.eq.1) then
!          Zeta as in Calculix and old ACC tool
         zeta=0.4d0*(1-W2W1)**2
         zeta=zeta*(W1W2)**2
!
!     Branch
      elseif(ichan_num.eq.2) then            
         hq=dh2/dh1
!
!        Interpolation as in CalculiX
         if((alpha.le.60.and.hq.le.1.d0).or.
     &      (alpha.le.90.d0.and.hq.le.2.d0/3.d0)) then
            zeta=0.95d0*((W2W1-2d0*dcos(alpha*pi/180))
     &                 *W2W1+1.d0)
            zeta=zeta*(W1W2)**2
         elseif(alpha.le.90.d0.and.hq.le.1.d0) then
            z2d390=0.95d0*((W2W1-2d0*dcos(90.d0*pi/180))
     &                 *W2W1+1.d0)
!
!            z1p090=0.95d0*(0.34d0+W2W1**2)
	    z1p090=0.95d0*(1.d0+0.3d0*W2W1**2)     
!
            z90=z2d390+(3*hq-2.d0)*(z1p090-z2d390)
!
            Z60=0.95d0*((W2W1-2d0*dcos(60.d0*pi/180))
     &                 *W2W1+1.d0)
!
            zeta=z60+(alpha/30.d0-2.d0)*(z90-z60)
            zeta=zeta*(W1W2)**2
	 elseif(alpha.le.60.d0.and.hq.gt.1.d0) then
!
!           extrapolation for hq>1 (not part of Idelchik
!           but the previous definition results sometimes 
!           into zeta<0 values
!	
            write(*,*)'WARNING in calc_residual_wye:'
	    write(*,*)'   Branch element is 
     &outside valid range defined by Idelchik'
            zeta=0.95d0*((W2W1-2d0*dcos(alpha*pi/180))
     &                 *W2W1+1.d0)
            zeta=zeta*(W1W2)**2	 
	 elseif(alpha.le.90.d0.and.hq.gt.1.d0) then
!
!           extrapolation for hq>1 (not part of Idelchik
!           but the previous definition results sometimes 
!           into zeta<0 values
!	
            write(*,*)'WARNING in calc_residual_wye:'
	    write(*,*)'   Branch element is 
     &outside valid range defined by Idelchik'
            Z60=0.95d0*((W2W1-2d0*dcos(60.d0*pi/180))
     &                 *W2W1+1.d0)
!
            z1p090=0.95d0*(1.d0+0.3d0*W2W1**2)    
!
            zeta=Z60+(z1p090-Z60)/(90.d0-60.d0)*(alpha-60)     
!                             
            zeta=zeta*(W1W2)**2	
!           interpolation between exit loss zeta=1
!           and last point of definition range (hq=1)
	    zeta=zeta+(1-zeta)/(50.d0-1.d0)*(hq-1) 	         
	 else
!	 
!	    values are absolutely out of def. range 
!	 
	    write(*,*)'ERROR in wye.f:' 
	    write(*,*)'   Branch element is 
     &outside valid range'
	    call exit(201)  
         endif
      endif
!
      zeta = zeta*zeta_fac
!
      if(icrit2.ne.1) then
         if(icrit1.ne.1) then
            f = pt2 - pt1*pspt1**zeta
         else
            f = xflow2*dsqrt(Tt1)/pt1/A2-Q_crit
         endif
      else
         f = xflow2*dsqrt(Tt1)/pt2/A2-Q_crit
      endif
!
      calc_residual_wye=f

      if(iflag.eq.4) then
!     Calculate Mach numbers
         call machpi(M1,pspt0,kappa,R)
         call ts_calc(xflow2,Tt2,pt2,kappa,r,A2,Ts2,icase)
!     Pressure ratio
         pspt2 = (Ts2/Tt2)**(kappa/(kappa-1))
         call machpi(M2,pspt2,kappa,R)
         
!         write(1,80)'Inlet: Tt1= ',Tt1,
!     &        ', pt1= ',pt1,', M1= ',M1
         
!         write(1,77)'mass flow = ',xflow2,', kappa = ',kappa,
!     &        ', zeta= ',zeta
         
!         write(1,80)'Outlet: Tt2= ',Tt2,
!     &        ', pt2= ',pt2,', M2= ',M2
         
 80      format(3x,a,f10.6,a,f10.2,a,f10.6)
 77      format(3x,a,f10.6,a,f10.2,a,f10.6)
      endif
!
      return
      end
